If You LOOK at This One ,
You see the adaptor nut - Goes Through the prop washer , equal to the washer thickness - length of shaft / saved .
A lot of the old diesels have a little spinner / nut . tommy bar or Hex aft .
Some Super Tigre early G 20/15 the nut secures a ' spinner ring ' around the prop , The fwd Spinner has the protrusion aft thru the rear coned ring.
Pretty much same idea as the photo .
Lees Machine Shop could whip you up something pronto .
Oliver Tigre & ETA 15 are similar ( pommy thread tho ). Better if protrusion length is just for though washer etc , not ALL the Prop .
The APCs are rebated in the front there anyway .
If youve got a prop reamer , . . . . .